The GAIA mission has led to a revision of the distance to L1157 by several groups [1]} and , who found \((360\pm 32)\hbox{\hspace{1.99997pt}pc}\)  and \((340\pm 21)\hbox{\hspace{1.99997pt}pc}\) , respectively. In this work, we will adopt the value of \((352\pm 19)\hbox{\hspace{1.99997pt}pc}\)  derived by [2]}, in agreement with [3]}. [4]}, [5]} have studied at high-angular resolution (\(\approx 3\) ) the structure and dynamics
of the southern lobe of the outflow driven by the protostar L1157-mm from the emission of the CO \(J\) =1–0 and SiO \(J\) =2–1 lines observed with the IRAM Plateau de Bure interferometer.
These authors showed that the southern lobe of this molecular outflow consists of two cavities, likely created by the propagation of large bow shocks due to episodic events in a precessing, highly collimated, high-velocity jet. This jet was detected by [6]} and imaged by [7]}. Based on higher-angular and high-sensitivity CO observations with NOEMA at \(0.3\) , [7]} refined the jet precession modelling by [4]} and estimated an age of \(\approx 1500\hbox{\hspace{1.99997pt}yr}\)  for B1 (and \(2500\hbox{\hspace{1.99997pt}yr}\)  for B2), adopting the new distance of \(352\hbox{\hspace{1.99997pt}pc}\) .
Located at the apex of the more recent cavity, the bright bow shock region B1 displays a peculiar molecular complexity [10]}, [11]}, which makes it a benchmark for magnetized shock models [12]}, [13]}, [14]}.
Multi-transition analysis of the emission of tracers such as CO [15]}, [16]}, H\(_2\) O [17]} and CS [18]}
has allowed to elucidate a coherent scenario where the molecular emission appears to arise from
four physically distinct components, with specific excitation conditions:
